GB2116407A - Electonically synthesised video palette - Google Patents

Description

1 GB 2 116 407 A 1

SPECIFICATION Electronically synthesised palette

The invention relates to image creation systems and more specifically to colour information synthesis suitable for use in such systems.

There are a number of standard computer peripherals available that permit "computer graphics" to be generated entirely electronically.

These can take the form of vector or raster displays with the input device usual in the form of a touch tablet on which the operator can draw and see the results of this work in real time on the electronic display.

A typical known electronic graphics system is shown in Figure 1, the main components comprising a touch tablet 10, a computer 12, a framestore 13 and a display 17. An artist draws with the stylus 11 of the touch tablet and the computer 12 registers the coordinates of the stylus whilst remembering the selected colour from selector 18 with which the artist has chosen to draw. The computer then feeds the appropriate addresses to the framestore 13 where the pixel at that address is modified to hold the code (typically 8 bits) corresponding to the chosen colour which it receives as incoming data. As the framestore is read at normal broadcast video rates under the control of the display address generator 15 typically locked to an external synchronising reference if available, then the lines, or pictures, drawn by the artist become visible on the display.

The monitor 17 is shown receiving the picture data converted into analogue form via DAC 14. It is found in practice that, providing the display is near to the touch tablet, the fact that the artist is not watching his hand but the screen provides no problem.

It is possible to use the computer to designate the stylus size via selector 19 so as to be several picture points in diameter for example so that the lines on the 'drawn' image will be of a designated width as though drawn with a larger stylus. This is achieved by controlling the writing of data into the frame store so that adjacent picture points receive the incoming data also.

Although the system shows a single frame store 13 for ease of understanding, in practice the colour information from computer 12 would typically be passed to three separate frame stores each handling respectively the luminance and colour difference components of the colour information (Y, 1 and Q for NTSC) and their outputs would be recombined to produce the normal colour information displayed on monitor 17 using standard video techniques. Alternative systems 120 using a single frame store are known where 1 partial colour' is handled in the form of Red, Green and Blue components of the colour information.

Although the colour is shown simply as being selected by selector 18, alternatively the operator, 125 when he desires to choose a colour, can call up an array of cells onto the monitor screen equivalent to a number of 'paint pots' and by moving the stylus over the touch tablet area can view the corresponding stylus position on the screen (as the computer typically generates a cross-wire or other screen cursor identifying the stylus position). When the stylus is located over the desired 'paint pot', the tablet is actually touched which then ensures that this is the colour selected by the computer for output to screen via the frame store as the stylus draws the desired image.

A problem with such systems especially where greater realism and more colour variations are desired is that the system must be designed to have a large number of such 'paint pots' available to the operator. Even then, the operator may find that the selection available is still not adequate for his needs.

The present invention is directed to an arrangement which allows the operator to produce any of a large variety of colours without the need to have unwieldy numbers of paint pots or other colour selector mechanisms.

The term 'colour' is used throughout the patent specification to encompass not only different colours but different hues of the same colour as well as different shades of grey in the monochrome medium.

According to the invention there is provided a synthesised palette comprising colour source means for defining at least two colours, selector means for selecting colours from the colour source means, processing means for mixing the selected colours in desired proportions, control means for manually controlling the desired proportions of the colour mix, monitor means for visually monitoring the mixing of the at least two colours, and holding means for retaining the mixed colour for use thereafter.

The invention will now be described byway of example with reference to the accompanying drawings, in which:

FIGURE 1 shows a known graphics system under manual control, FIGURE 2 shows an embodiment of the synthesised palette of the present invention, FIGURE 3 shows the palette display with a mix of colours thereon, FIGURE 4 shows colour processing in the form of three component paths operating simultaneously, and FIGURE 5 shows a palette arrangement suitable for incorporating into the Figure 1 system.

An embodiment of the synthesised pallette of the present invention is shown in Figure 2. In this embodiment the palette will be operating in the digital domaine.

The palette system includes a number of 'paint' colours from colour sources 20-23. Typically each of these sources can comprise a digital thumbwheel switch producing a digital output indicative of the colour allocated thereto. Each switch typically will have more than one position so as to provide a selection of colours. One of the appropriate colours can be accessed via rotary switch 24 and the digital number is passed to processor 30 consisting in this arrangement of a subtractor 32, multiplier 33 and adder 34. The 2 GB 2 116 407 A 2 processed output is made available to one or more of the locations within palette store 31 under the control of palette store address generator 35. The addresses are designated by the stylus 11 contacting the touch tablet 10 as in the Figure 1 arrangement, although the palette store need not be as large as the frame store and thus the pixel addressing requirements can be reduced.

The touch tablet provides a strobe every time the pen is moved and this is used to initiate a 75 palette store write cycle.

Typicaily the palette size can be 256 x 128 pixels thus giving a 1/1 6th screen size palette area when displayed on the monitor. The colour mix provided by processor 30 at any point within the palette as monitored via store 31 can be retained for future use when actually 'painting' by passing the digital equivalent to latch 27, 28 or 29 via switch 25, the relevant pixel location being chosen by placing of the stylus 11 on the appropriate location on the touch tablet 10 whereby that palette address can be accessed.

In practice stylus 11 is typically fabricated to include a pressure sensitive device (e.g. spring loaded potentiometer) so that the pressure applied 90 produces a voltage which after conversion in ADC 28 is used to manipulate the processing within processor 30 jo as to simulate more closely the mixing effect associated with paint mixing on a normal palette and as illustrated in Figure 3.

More thar one colour from the blend may be rat tained in the spare latches. Thus a typical operation of the palette system would commence with selecting colour 1 say and 6ntering this onto the palette, that is via processor 30 into store 3 1.

As no other colour will be present in store 31 at this stage the colour stored will be dependent on the s--tyiiis pressure a!o--,e. On selecting colour 2 as shown in Figure 2, this colour is processed with the stored colour so as to blend in those portions where the two colours overlap. This mix will also 105 depend on the. stylus pressure and how many overstrokes of the stylus have been made by the operator. When a particular colour or range of coiours have been satisfactorily produced then each of these (e.g. colour M and N of Figure 3) can 110 be retained in the appropriate latches for further use either for painting or for blending with other coloers via switch 24. This technique allows a whole range of colours to be generated at will from a few basic colours. Although only three latches are shown for simplicity this number can be increased. Thus when an operator is working on faces for example a range of flesh tones can be built up and retained for use on that particular subject. Where another picture is concerned with 120 sky rendering then a range of blues can be used.

Although the system has been described as simulating the normal paint mixing process it could be modifed so that the touch tablet produces a steady stream of strobes so that the mixing effect takes into account the time period for which the stylus is held at a given location.

Although the paint colour processing has been illustrated in terms of a single processor 30 and palette store 31 for simplicity of understanding (and which would be perfectly adequate for monochrome pictures where the colours produced were all shades of grey), in practice the colour information will typically be handled in three identical paths. Thus as shown in Figure 4 the paint colour from blocks 20A, 2013, 20C, which respectively hold the colour components (e.g. Y, 1 and Q) will be output to respective processors and palette stores 30A-30C, 3 1 A-31 C driven in parallel from common address generator 35. The respective outputs will pass to combiner 43 where full colour will be provided for monitoring (via a digital to analogue converter as necessary) or can be fed back to holding latches.

Where the palette system of the invention is incorporated into an existing graphics arrangement of the type shown in in Figure 1 then the present system can be represented by the Figure 5 arrangement. A selected colour made available via the computer can be mixed with a colour already present in the palette and after mixing the colour of interest can be retained in latch 26 for use in the frame store.

Although not shown it may be convenient to blank the monitor screen for that area outside the palette area, using standard techniques, or to key the palette area over the picture being painted.

Although the palette system of the invention is suitable for basic graphics generators, the flexibility and capability of the palette makes it ideal for more sophisticated systems such as that described in co-pending U.K. patent application no. 8136539.

Claims (17)

1. A synthesised palette comprising:

colour source means for defining at least two colours, selector means for selecting colours from the colour source means, processing means for mixing the selected colours in desired proportions, control means for manually controlling the desired proportions of the colour mix, monitor means for visually monitoring the mixing of the at least two colours, and holding means for retaining the mixed colour for use thereafter.

2. A palette as claimed in claim 1, wherein the processing means includes a palette store having a plurality of locations adapted to define the palette mixing area.

3. A palette as claimed in claim 2, wherein the processing means including said palette store includes a plurality of processing paths adapted to simultaneously handle designated components of the colour information.

4. A palette as claimed in claim 2, wherein the control means is adapted to manually control the portion of the palette area used in the colour mixing process and to control access of the colour retained by said holding means.

5. A palette as claimed in claim 1, wherein the control means includes a manually operable 11 3 GB 2 116 407 A 3 sensor for varying the mixing effected by said processing means.

6. A palette as claimed in claim 5, wherein the sensor is adapted to vary the mixing affected in dependence on manual pressure applied thereto.

7. A palette as claimed in claim 1, wherein the processing means includes at least one adder and multiplier.

8. A palette as claimed in claim 1, wherein the control means includes a touch tablet with associated stylus adapted to control the application of the selected colours.

9. A palette as claimed in claim 1, wherein the holding means includes a plurality of data latches each for holding information representative of the mixed colour.

10. A palette as claimed in claim 3, wherein the colour source means includes a plurality of sources each for designating a component of the colour information for use in the respective processing paths.

11. A palette as claimed in Claim 2, wherein the mixing process is adapted to take into account the time period for which the control means is held at a given location.

12. A method of synthesising a palette comprising the steps of defining at least two colours, selecting a colour from the defined colours, mixing the colours in desired proportions under manual control, monitoring the mixing process and retaining the mix when the desired colour has been obtained.

13. A method as claimed in claim 12, including the step of defining the palette mixing area to be of such a size as to allow variations in the mix to be obtained.

14. A method as claimed in claim 12, including the step of varying the colour mix in dependence.

on manually applied pressure.

15. A method as claimed in claim 12, including the step of dividing the mixing process into a plurality of paths so as to allow designated components of the colour to be processed simultaneously.

New claims or amendments to claims filed on New claims:- 16,17

16. A synthesised palette, substantially as described herein and as illustrated in the accompanying drawings.

17. A method of synthesising a palette substantially as described herein.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1983. Published by the Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.